An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• give the four-membered ring intermediate 29. Finally, the rearrangement of the four-membered intermediate provides the diketone 30 as the product (Scheme 8). In 2017, Wang and co-workers reported an oxidative cleavage of aromatic alkenes at ambient temperature with visible-light irradiation, using

• generates the active species Mes–Acr–Me*. Then, the single-electron oxidation of the deprotonated carboxylic acid 52 with Mes–Acr–Me* results in the formation of an acyloxyl radical 53. The subsequent rearrangement of the radical 53 gives a carbon-centered radical 54 and carbon dioxide. The phenyl thiyl

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• underwent a thermal rearrangement to generate tricyclic isobenzofurans 313 through the ring-cleavage of the thietanes. It was assumed that the rearrangement was assisted through participation of the oxygen lone-pair electrons [17] (Scheme 57). The silicon-containing phenyl triphenylsilyl thioketone (316

• -haloalkyl)thiiranes: A thiirane–thietane rearrangement took place upon the interaction of (1-haloaklyl)thiiranes 398 with hard and weak nucleophiles (:Nu−) in the presence of a base. It was an efficient method for the preparation of 3-substituted thietanes 400 from (1-haloalkyl)thiiranes 398 through an

The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts

• Svetlana A. Kuznetsova,
• Alexander S. Gak,
• Yulia V. Nelyubina,
• Vladimir A. Larionov,
• Han Li,
• Michael North,
• Vladimir P. Zhereb,
• Alexander F. Smol'yakov,
• Artem O. Dmitrienko,
• Michael G. Medvedev,
• Igor S. Gerasimov,
• Ashot S. Saghyan and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2020, 16, 1124–1134, doi:10.3762/bjoc.16.99

• nondirectional forces in the crystal whilst leaving the directional hydrogen bonds still present so that the framework remained heterogeneous. Notably, simple organic cages that exhibit guest-induced “breathing” and selective gas separation have been reported [29][39][40][41]. The reversible rearrangement of the

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• ‑hydroxy-β-aminophenylalanine esters [75][76] 152a–d using XtalFluor-E. The reaction also included an aziridinium ion rearrangement as the key step. Deprotection of the resultant β-fluoro-α-amino acid esters 153a–d afforded the corresponding enantiopure anti-β-fluorophenylalanines 154a–d in good yield and

Accelerating fragment-based library generation by coupling high-performance photoreactors with benchtop analysis

• Quentin Lefebvre,
• Christophe Salomé and
• Thomas C. Fessard

Beilstein J. Org. Chem. 2020, 16, 982–988, doi:10.3762/bjoc.16.87

• preliminary quality control (QC) could be performed using a benchtop 60 MHz NMR machine (Figure 3). Structural information was obtained to corroborate mass spectrometry data, an important information when dealing with strained bicycles or spirocycles, which could be prone to skeletal rearrangement. If

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• superoxide radical anion by a reductive quenching and the rearrangement of the hydroperoxide intermediate [41]. The heterogeneous protocol using MOF porphyrins was significantly faster than the corresponding homogeneous photocatalysis, which was attributed to higher photostability of the porphyrins as MOF

• photooxygenation reactions were described using TPP as photocatalyst. We have described a study on endoperoxydations followed by rearrangement to yield naphthoquinones starting from α-naphthols and using porphyrins as photocatalysts (Scheme 36) [23]. Eleven examples were described from mg to g-scale reactions, and

• conditions, a porphyrin-based protocol for endoperoxidation of the diene, followed by the Kornblum–DeLaMare rearrangement and further telescoped transformations. This protocol yields different classes of products such as furans, tropone, diketones and hydroxyenones, all of them starting from the

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• -butyl ketone (1) yields acetone (4) and propylene (3). Reaction (2) of Scheme 1 refers to a type II intramolecular rearrangement of crotonaldehyde (5) to 3-butenal (7). The triplet state energy donors were quenched by diacetyl and cis-2-butene. In 1970, Cocivera and Trozzollo studied the photolysis of

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• Analytical Chemistry, University of Debrecen, H-4032 Debrecen, Hungary 10.3762/bjoc.16.75 Abstract A series of 1-substituted-3-methyl-2-phospholene oxides was prepared from the corresponding 3-phospholene oxides by double bond rearrangement. The 2-phospholene oxides could be obtained by heating the 3

• thermal conditions, in the presence of acids or bases or via the formation of chlorophosphonium salts. In our study, the 3-methyl-3-phospholene oxides were considered as model compounds, the double bond rearrangement of a 3-phospholene oxide and a 3,4-dimethyl-3-phospholene oxide was also investigated

• rearrangement, involving zwitterionic structure 11 via high energy and a four-membered ring transition state [TS(1→11)]. This stressed structure has a rigid, entropically unbeneficial transition. The second transition state [TS(11→4)] represents a significantly lower energy gap with a more comfortable five

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• coordinated to the metallacarbene and cleaved (Scheme 3 (a)) and the formed alkylidene species is inserted into the alkyne unit through a metallacyclobutene intermediate. This metallacyclobutene, through the rearrangement to a vinyl metal-alkylidene (Scheme 3 (b)) and subsequent metathesis with the alkene

• on a Diels–Alder cycloaddition, an intramolecular Mitsunobu reaction, a [3,3]-sigmatropic rearrangement, and a ring-closing metathesis. As an alternative to this approach, Clark et al. [86] efficiently performed a sequential Ru-catalyzed enyne metathesis in combination with a hydroboration, and an

• of cyclopentene-1,4-diol that was obtained by the enzymatic desymmetrization of the corresponding diacetate, an enyne metathesis precursor was accessed by a Mitsunobu-type coupling reaction with propargylic amide. The ring-rearrangement metathesis (RRM) of this enyne precursor was carried out using

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• rearrangement to form a C–Cu bond-containing intermediate 78 (Scheme 17A). The O–Cu intermediate 77 can be intercepted either by PhMe2SiBpin or methanol to give the silylated O-Bpin product 79 or silyl alcohol 80, respectively. Interestingly, it was eventually realized that the use of the NHC ligand is not

• intermediate. This species then undergoes [3,3]-sigmatropic rearrangement, positioning the allylic unit in a regio- and stereospecific manner, along with rearomatization to afford the products 357–360 (Scheme 57) [107]. The borylfluoromethylation of acrylamides, acrylates, and heteroaromatic-substituted alkenes

• was observed. Due to the possibility of facile rearrangement of the former to the latter, it could not be concluded that a direct insertion of the aldehyde into the Cu–B bond is taking place. The enantioselective borylation of aliphatic aldehydes 448 was first reported in 2015 using CuCl/KO-t-Bu/(R

Synthesis of C₇₀-fragment buckybowls bearing alkoxy substituents

• Yumi Yakiyama,
• Shota Hishikawa and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2020, 16, 681–690, doi:10.3762/bjoc.16.66

• and optical properties were investigated by single crystal X-ray analysis and UV–vis spectroscopy. In the synthesis of dioxole derivative 5b, the regioisomer 5c was also produced. The yield of 5c was increased by increasing the reaction temperature, indicating that the rearrangement might involve the

• equilibrium between the Pd(IV) intermediates through C–H bond activation. Keywords: buckybowl; C70; rearrangement through C–H bond activation; Introduction The study of buckybowls, the bowl-shaped π-conjugated aromatic hydrocarbons corresponding to the fragments of fullerenes, pioneered by the works on

• expansion by Wagner–Meerwein rearrangement, followed by Pd-catalyzed annulation (Figure 1) [18]. An UV–vis spectroscopy study revealed that the electronic character of 1 rather resembled that of an indenopyrene moiety than that of benzopyrene. Our synthetic route allows to easily introduce substituents on

Regio- and stereoselective synthesis of new ensembles of diversely functionalized 1,3-thiaselenol-2-ylmethyl selenides by a double rearrangement reaction

• Svetlana V. Amosova,
• Andrey A. Filippov,
• Nataliya A. Makhaeva,
• Alexander I. Albanov and
• Vladimir A. Potapov

Beilstein J. Org. Chem. 2020, 16, 515–523, doi:10.3762/bjoc.16.47

• potassium selenocyanate proceeded via a rearrangement with ring expansion, leading to a six-membered 2,3-dihydro-1,4-thiaselenin-2-yl selenocyanate (kinetic product) which in turn underwent rearrangement with ring contraction to a 1,3-thiaselenol-2-ylmethyl selenocyanate (thermodynamic product). These

• -thiaselenole; nucleophilic addition; nucleophilic substitution; rearrangement; seleniranium intermediate; Introduction The regio- and stereoselective synthesis of organoselenium compounds based on selenium-centered electrophilic reagents has been one of the most important and effective directions in

• -dihydro-1,4-thiaselenines (up to 96% yields) – products of rearrangement with ring expansion, which in turn underwent rearrangement with ring contraction, forming a new family of 1,3-thiaselenoles in up to 99% yield. The article was included in the RSC themed web collection "The chemistry of Selenium

KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones

• Qiao Lin,
• Shiling Zhang and
• Bin Li

Beilstein J. Org. Chem. 2020, 16, 492–501, doi:10.3762/bjoc.16.44

• nitrogen to benzyl bromide would form an ammonium intermediate C. The final product 3a would be produced after rearrangement and release of tert-butyl bromide. On the other hand, added I2 would react with intermediate B’ and lead to the thiazolidone compound 5a. Conclusion In summary, we have developed a

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• -photocatalyzed intramolecular decarboxylative C–N coupling of NHP esters using an in situ-formed heteroleptic copper complex (Scheme 23) [38]. This protocol, a versatile alternative to the Curtius rearrangement, was applied to a large variety of substrates, including primary/secondary alkyl, cycloalkyl, and

Six-fold C–H borylation of hexa-peri-hexabenzocoronene

• Mai Nagase,
• Kenta Kato,
• Akiko Yagi,
• Yasutomo Segawa and
• Kenichiro Itami

Beilstein J. Org. Chem. 2020, 16, 391–397, doi:10.3762/bjoc.16.37

• functionalizing poorly soluble compounds, functionalized HBC is typically synthesized by dehydrogenative cyclization, which is called Scholl reaction, of precursors having solubilizing substituents [12][13]. However, the Scholl reaction sometimes causes unexpected rearrangement such as 1,2-aryl shift, and

Allylic cross-coupling using aromatic aldehydes as α-alkoxyalkyl anions

• Akihiro Yuasa,
• Kazunori Nagao and
• Hirohisa Ohmiya

Beilstein J. Org. Chem. 2020, 16, 185–189, doi:10.3762/bjoc.16.21

• rearrangement and then successfully trapped with aryl bromides under palladium catalysis (Scheme 1). This system was extended to an asymmetric version using the chiral α-silyloxybenzylcopper(I) species having a chiral NHC ligand. In the asymmetric system, one example of allylic carbonate was used as the carbon

• silyl ether, which are derived from the Pd-catalyzed allylic silylation of 2a and the Cu-catalyzed silylation of 1a and the subsequent [1,2]-Brook rearrangement, respectively. In this coupling reaction, (SIPr)CuCl was a slightly better copper complex than (IPr)CuCl (62%), (SIMes)CuCl (60%) and (IMes

• ) species B. The 1,2-addition of silylcopper(I) B to the aromatic aldehyde 1 [15][16][17][18][19] and the subsequent [1,2]-Brook rearrangement from the obtained α-silyl-substituted copper(I) alkoxide C forms the key intermediate, an α-silyloxybenzylcopper(I) species D. The transmetallation between D and an

Efficient method for propargylation of aldehydes promoted by allenylboron compounds under microwave irradiation

• Jucleiton J. R. Freitas,
• Queila P. S. B. Freitas,
• Silvia R. C. P. Andrade,
• Juliano C. R. Freitas,
• Roberta A. Oliveira and
• Paulo H. Menezes

Beilstein J. Org. Chem. 2020, 16, 168–174, doi:10.3762/bjoc.16.19

• there are several stereoselective methods described for the reaction of propargyl or allenyl organometallics with carbonyl compounds [8][9][10][11][12][13][14], the control of the regioselectivity is still a major concern. This is mainly due to the metallotropic rearrangement of propargyl and allenyl

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• reaction. In the presence of a Brønsted acid, mainly [1,3]-rearrangement is observed, whereas a Lewis acid catalyzes the [1,4]-sulfur migration. To gain insight into the mechanism of these transformations, the stereochemistry of these rearrangements have been tested, along with the conduction of some

• control experiments and DFT calculations. Keywords: Brønsted and Lewis acids; DFT; mechanistic studies; rearrangement; stereochemistry; sulfur atom migration; Introduction Among all organic reactions, rearrangements are an exciting class of transformations where unusual or even unexpected products can

• many others. In organophosphorus chemistry, rearrangements are less developed transformations, however, some examples can be found in the literature (Scheme 1). These include the famous Arbuzov rearrangement [29][30][31][32] as well as phospha-Fries ([1,3]-rearrangements) [33][34][35][36][37], phospha

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• Bratislava, Mlynská dolina, Ilkovičova 6, 84215 Bratislava, Slovakia 10.3762/bjoc.15.290 Abstract A range of chiral hydrogen-bond-donating organocatalysts was tested in the Ireland–Claisen rearrangement of silyl ketene acetals. None of these organocatalysts was able to impart any enantioselectivity on the

• rearrangements. Furthermore, these organocatalysts slowed down the Ireland–Claisen rearrangement in comparison to an uncatalyzed reaction. The catalyst-free reaction proceeded well in green solvents or without any solvent. DFT calculations showed that the activation barriers are higher for reactions involving

• hydrogen-donating organocatalysts and kinetic experiments suggest that the catalysts bind stronger to the starting silyl ketene acetals than to transition structures thus leading to inefficient rearrangement reactions. Keywords: DFT calculations; green solvents; H-bonding catalysts; Ireland–Claisen

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• further oxidation to carbonyls or carboxylates. Other reactions, such as epoxidation, ether bond formation, and structural rearrangement have also been reported (Figure 7). CYP114 in gibberellin (5) biosynthesis, for example, catalyzes the unique oxidation/six-membered to five-membered ring contraction of

• examples of terpene modification by bacterial CYPs. a) Hydroxylation [89]. b) Carboxylation, hydroxylation, and ring contraction [41]. c) Ether formation [90]. d) Rearrangement [91]. Off-target effects observed during heterologous expression of terpenoid BGCs. Unexpected oxidation of 34b by an

Facile regiodivergent synthesis of spiro pyrrole-substituted pseudothiohydantoins and thiohydantoins via reaction of [e]-fused 1H-pyrrole-2,3-diones with thiourea

• Aleksandr I. Kobelev,
• Nikita A. Tretyakov,
• Ekaterina E. Stepanova,
• Maksim V. Dmitriev,
• Michael Rubin and
• Andrey N. Maslivets

Beilstein J. Org. Chem. 2019, 15, 2864–2871, doi:10.3762/bjoc.15.280

• pyrrole-2-one fragment involving the reaction of [e]-fused 1H-pyrrole-2,3-diones with thioureas was developed. The obtained spiro pseudothiohydantoin derivatives were found to undergo a pseudothiohydantoin–thiohydantoin rearrangement. The reactions were shown to proceed under catalyst-free conditions in

• good yields, and the products were isolated without applying preparative chromatography methods. Keywords: diversity-oriented synthesis; hydantoin; nitrogen heterocycles; rearrangement; thiourea; Introduction Hydantoin (imidazolidine-2,4-dione) derivatives are omnipresent among biologically active

• rearrangement (PTR, Scheme 1) [8][9][10][11], which is a special case of a quite poorly investigated iminothiolactone–thiolactam rearrangement [12][13][14][15][16]. This reaction offers attractive opportunities for the design of libraries of regioisomeric hydantoin-based compounds for drug discovery. Spiro

One-pot synthesis of substituted pyrrolo[3,4-b]pyridine-4,5-diones based on the reaction of N-(1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-oxo-2-arylethyl)acetamide with amines

• Valeriya G. Melekhina,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Vitaly S. Mityanov,
• Artem N. Fakhrutdinov,
• Arkady A. Dudinov,
• Vasily A. Migulin,
• Yulia V. Nelyubina,
• Elizaveta K. Melnikova and
• Michail M. Krayushkin

Beilstein J. Org. Chem. 2019, 15, 2840–2846, doi:10.3762/bjoc.15.277

• formation of various nitrogen-containing heterocycles [11][12][13][14][15][16]. In order to investigate the possibility of an analogous rearrangement of the pyranone ring in 2 when being attached by an amine, we studied the model reaction of N-(2-(4-chlorophenyl)-1-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• Sarah L. Skraba-Joiner Carter J. Holt Richard P. Johnson Department of Chemistry and Materials Science Program, University of New Hampshire, Durham, NH 03824, USA 10.3762/bjoc.15.258 Abstract Arenes undergo rearrangement of phenyl, alkyl, halogen and other groups through the intermediacy of ipso

• . DFT computations with inclusion of implicit solvation support a complex network of phenyl and biphenyl shifts, with barriers to rearrangement in the range of 10–21 kcal/mol. Consistent with experiments, the lowest energy arenium ion located on this surface is due to protonation of m,p'-quaterphenyl

• . This supports thermodynamic control based on carbocation energies. Keywords: arenium ion; carbocation; density functional theory; microwave reaction; rearrangement; superacid; Introduction Carbocations are enigmatic reactive intermediates of enduring importance in chemistry. No other reactive species

Synthetic terpenoids in the world of fragrances: Iso E Super^® is the showcase

• Alexey Stepanyuk and
• Andreas Kirschning

Beilstein J. Org. Chem. 2019, 15, 2590–2602, doi:10.3762/bjoc.15.252

• ) and β-pinene (8), 3-carene (20), limonene (6) and camphene (21). Since no large-scale source for myrcene (1) was available, a short route from readily available monoterpenes was established. Under pyrolytic conditions β-pinene (8) as constituent of turpentine undergoes a rearrangement to myrcene (1

Safe and highly efficient adaptation of potentially explosive azide chemistry involved in the synthesis of Tamiflu using continuous-flow technology

• Cloudius R. Sagandira and
• Paul Watts

Beilstein J. Org. Chem. 2019, 15, 2577–2589, doi:10.3762/bjoc.15.251

• effort to address the safety concerns raised by the potentially explosive acyl azide 1a (Scheme 1), Hayashi and co-workers [14] demonstrated the handling of the Curtius rearrangement reaction (transformation from acyl azide 1a to isocyanate 1b) in a microreactor system (Scheme 1 and Figure 1). Acyl azide

• compound 2 from acyl chloride 1 via Curtius rearrangement using a continuous-flow system [14]. Continuous-flow system for C-3 azidation of mesyl shikimate using aqueous sodium azide. Mesyl shikimate azidation conversion in a continuous-flow system using NaN3. Desired azide 5 selectivity in a continuous